Back lighting of a display surface has been typically accomplished by using a reflecting light box having a light source positioned behind the display surface. The distance of the light source from a display surface is critical in order to avoid hot spots which are observable bright spots caused by the light source. However, due to physical restrictions, the space for a light box is not always available.
Space restrictions have been accommodated to some degree by utilizing light piping and wedge lighting. According to light piping techniques, light rays from a light source are conducted by light pipes to the display surface. Light piping techniques are illustrated in U.S. Pat. Nos. 3,632,938 and 3,718,814. According to wedge lighting, an acrylic wedge that is edge lit by a light source, is placed behind the display surface. Wedge lighting techniques are illustrated in U.S. Pat. No. 3,617,727. Although size reductions can be obtained by using light piping and wedge lighting techniques, these techniques do not eliminate hot spots while still brightly lighting the display surface under high ambient light conditions.